1. Field of the Invention
The present invention pertains to a drive mechanism for a lens member in which an electro-mechanical transducer is used.
2. Description of the Related Art
In a lens requiring a long lens mount, such as a photo-taking lens having a long focal length, a collapsible lens mount comprising multiple mount parts, which is collapsed when not in use and which is extended when it is used, may be used.
In a zoom lens system in which the focal length may vary, the construction is such that some of the multiple optical elements (lens units) comprising the entire lens system are moved along the optical axis, so that the focal length changes.
In such a zoom lens system, moreover, because the angle of view changes in response to the focal length, an extendable hood may be used, the position of which along the optical axis may be changed in accordance with the change in the angle of view.
Multiple complex cam mechanisms have been in use to drive said conventional collapsible mount, the optical elements of the zoom lens system, the lens hood, etc. As a consequence, the size of the camera becomes large, and cost disadvantages exist as well. In addition, while multiple cam mechanisms are used to drive optical elements comprising a zoom lens system, some of the optical elements require a minute change in position. However, it has been difficult to achieve these minute changes in position with sufficient precision using cam mechanisms.
Therefore, an efficient drive means has been sought which does not require a large amount of space for the drive of the lens system components such as the lens mount, optical elements and lens hood, and which is capable of freely carrying out minute as well as large changes in the positions of the optical elements.
The phrase `lens members` refers to various members including lens mounts which directly support the lenses, lens mounts which indirectly support the lenses, and lens hoods, as well as the lenses themselves. The lens assembly comprising these lens members is called the `lens system`.